I agree with @taskmaster4450 that limiting number of posts isn't the answer. There will be a handful of talented folk who can kick out more than 4 high quality posts in a day and I think it would be a shame to enforce arbitrary limits and deny this creativity and freedom of expression.

I personally believe that the solution lies in tackling self-voting and this needs to be addressed with some sort of max vote amount and degradation in value over say a 24 hr period. Say 100%-80%-60% etc per post down to 0%. So you would put your best efforts into your first 3-4 posts per day (which feeds into your suggestion by a different route) as you know the next 5-6 aren't going to get (as) much on your self-votes. Maybe start with a $100 max self-vote at 100%. For those who aren't in it to milk the system, they can quite happily carry on posting in a day beyond this limit and will have to rely on the voting public for any further upvotes. (what this doesn't tackle is collusion...suggestions please!).

Just a thought.